Extraordinary landscape photography from Colorado and the West

The Best App for Sun and Moon Position Search

Updated: Apr 8

Planning a shot that includes the sun, moon, or Milky Way? Sun Surveyor, available for both iOS and Android, makes it easy.

Moonset over Longs Peak, Rocky Mountain National Park, Colorado

My first attempt at shooting the full moon setting over Longs Peak at sunrise was a fiasco. I got up at 2 a.m., hiked three hours in the dark to the summit of Twin Sisters, and discovered that the moon was so far to the right of Longs Peak that it was no bigger than a dust speck when I attached the 35mm lens I needed to include both mountain and moon. Longs Peak was not much bigger.

That misadventure convinced me I needed to plan such shoots much more carefully if I was going to have something to show for a night of lost sleep. My goal was to identify days when the moon would be near the horizon and setting directly over Longs Peak at the moment of sunrise. Selecting the best dates required a table of moon positions, a USGS topographic map, a compass, a ruler, and a scientific calculator to handle the trigonometry calculations. A student in one of my workshops, Stephen Trainor, saw the value in my careful planning but considered my methods hopelessly inefficient. He went home and developed a piece of software he named the Photographer’s Ephemeris (TPE), available for Apple and Android devices as well as desktops and laptops. TPE is a brilliant piece of software that I use constantly. It has greatly simplified the planning process, but the current version still has one weakness. The ability to search for specific positions of the sun and moon is limited to the iOS version, and even on that platform its search capabilities can only narrow down the range of possible dates. Picking the best date still requires a lot of cross-checking. PhotoPills (iOS and Android, no desktop version) also has search capabilities, but again the results must be checked one-by-one to identify the best day.

At this time, Sun Surveyor has the most sophisticated sun/moon search capabilities available. To understand the power of developer Adam Ratana's solution, think a bit more about the problem of shooting the full moon setting over Longs Peak from Twin Sisters. First, you need to know the direction of Longs Peak from Twin Sisters, information you can most easily obtain from TPE on a desktop computer, but that you can also obtain from Sun Surveyor or an old-fashioned paper map and a compass. That direction – the azimuth – turns out to be about 245 degrees. Obviously, the moon doesn’t need to be precisely over Longs Peak for the photo to work. There is some range of acceptable azimuths. Let’s say the usable range is 235 to 250 degrees.

Next, you need to know how much you must look up to see the summit of Longs Peak when you’re on the summit of Twin Sisters, which is lower than Longs Peak by about 2,800 feet. Again, TPE takes all the math out of the calculation. With the primary marker on the summit of Twin Sisters, drop the secondary marker on the summit of Longs Peak and check the geodetic panel. The altitude (angular elevation) Longs Peak is about 6 degrees. Obviously, the moon must have an altitude of 6 degrees or more to be visible above the actual horizon. Again, however, there is an acceptable range of altitudes. The moon subtends an angle of just 0.5 degrees. A moon that is 4 degrees above the summit of Longs Peak is eight moon diameters above the ridgeline. Much higher than that, and the moon will be very small when you use a lens that includes both Longs Peak and the moon. Let’s say the acceptable altitude range is 6 to 10 degrees.

We’re almost there. We have two other considerations: the percentage of the surface of the moon that will be illuminated, and when the moon will appear within the acceptable range of azimuths and altitudes. We’re looking for a full moon, so a percentage illumination of 95 to 100 percent is appropriate. And we want beautiful light, so the range of acceptable times is from about 10 minutes before sunrise, when the twilight wedge will be approaching its peak, until about 10 minutes afterwards, when the warmth of the sunrise light will have largely faded. If you were shooting the full moon rising at sunset, you’d want a similar time range around sunset.

The beauty of Sun Surveyor is that it allows you to enter each of these search parameters as a range: azimuth, altitude, percentage of moon illuminated, and time in relation to sunset or sunrise. First, locate the Position Search screen by choosing the map module from the main menu, then swiping across the Info Carousel just below the map (figure 1). Tap the Location icon in the top right corner of the Map module (again figure 1; the shape of the icon will vary depending on which device you're using) and search for the location of your shooting position, in this case, Twin Sisters.

Figure 1. The Map module in Sun Surveyor.

Now enter the parameters listed above on the Parameters screen (figure 2). Choose how many months you want to examine and tap Search. If you’ve entered your search parameters correctly, then every day in the search results will work, but you can use TPE to double-check and pick the very best day. In this example, choosing a day when the moon will appear over the notch between Longs Peak and Mt. Meeker at sunrise will produce a strong “triangular” composition, with three major points of interest: the moon, Longs Peak, and Mt. Meeker. Add some warm light at sunrise and you’ve got a winner.

Figure 2. The Search Parameters screen in Sun Surveyor.

Figure 3. The Search Results screen in Sun Surveyor.

Using the criteria listed here, the best dates in 2020 for this shot are May 8 and August 4. Mark your calendars!

Sun Surveyor also lets you search for specific positions of the sun by entering an appropriate range for altitude and azimuth. And you can search for specific positions of the galactic center, the most photogenic part of the Milky Way, by entering a range for altitude and azimuth and specifying that the results only include periods between astronomical dusk and dawn with no moon.

No photographer can afford to be in the field 365 days a year. Thoughtful use of Sun Surveyor will help you choose the most promising days to get out and shoot. And if this level of planning sounds like a bit much right now, check out Sun Surveyor’s new Opportunities screen, also found on the Info Carousel, which lists upcoming dates with photographic potential. Opportunities includes dates when either the full moon or new moon will be near the horizon at sunrise or sunset, and dates and times when the galactic center, the most photogenic part of the Milky Way, will be above the horizon during periods of total darkness and no moon. You can even customize the criteria Sun Surveyor uses to identify opportunities. Sun Surveyor has made it easier than ever to be in the right place at the right time.